Large C-frame, Gemcor Riveters, for example, are used to drill holes and install fasteners in aircraft. Some fasteners require a sealant between a countersink surface of a fastener, as a rivet, and a countersunk surface of an aircraft skin in which the rivet head fits. The sealant is required for corrosion protection. The sealant is typically dispensed from a Semco glue gun. This type of glue gun has a relatively large cartridge with a piston to push the sealant. It also has a valve to introduce high pressure air behind the piston in order to urge the sealant out the dispensing end of the glue gun. The present guns do not have means for precise volume control of the sealant dispensed. Therefore, the sealant frequently is dispensed in either too large a quantity or too small a quantity.
The variations in quantity are sometimes related to a change in viscosity that takes place as the sealant begins to set during dispensing. Both of the extremes in quantity create lost time and extra cost. If too much sealant is dispensed, then the airplane parts are contaminated and must subsequently be cleaned. If too small a quantity is dispensed, then rework is required. Thus, there has been a need for a sealant dispensing system to provide precise quantity control of the sealant dispensed and which is independent of any changes in viscosity.
There are four known types of dispensing systems of which applicant is aware. The first one is that indicated above. It consists of a relatively large cartridge and piston and as indicated the system is not precise. Its dispensed quantity varies with the viscosity, and most of the sealant is wasted in that it sets in the cartridge before it can be dispensed.
A second system employs a peristaltic-type pump and it is good for continuous flow-type operations with large volumes, but does not work for small quantities. The peristaltic-type pump consists of a plastic tube which is contained within a semicircle cylindrical enclosure and then squeezed by rollers. This introduces a pinching action which forces liquid to travel within the plastic tube. The problem with this system is that no means are presently available to drive the rollers for precise increments, and even if there was, the volume dispensed would vary when the rollers engage and disengage the tube.
Two other commercially available systems are used for dispensing small quantities of sealants or adhesives. The first one is a sophisticated control box applied to another cartridge piston arrangement only with smaller cartridges. This system has the same problems as the cartridge piston system described above. The other system includes a precision screw motor used to push a screw which in turn pushes a piston inside a cartridge. The problems with this system are primarily with the awkwardness of the controls, clean-up, large size, and cost.
A search of the patent literature discloses positive displacement pumps having a rod which is driven by friction clamp means. For example, in U.S. Pat. No. 2,726,802 to Jones, for a Loading Rig for Caulking Guns there is a piston rod 26 which passes through a hole in a plate 33 and mounted on the plate is an upper coil spring 34 which is surmounted by double washer assembly 35. Both spring 34 and washer assembly 35 surround the rod 26, the spring biasing the washer into contact with a pintle 36. In consequence of the non-central location of the pintle 36 and the action of coil spring 34, washer assembly 35 assumes the inclined position shown in FIG. 1 in which the edges of the washer assembly surrounding the hole therein bite into operating rod 26, thereby effectively precluding upward movement but nevertheless permitting limited downward movement of the rod. Immediately below the plate 33 is a similarly shaped double washer assembly 37 that is biased toward a horizontal position by an underlying coil spring 38 surrounding operating rod 26. Like washer assembly 35, washer assembly 37 is provided with a central hole through which operating rod 26 passes. Such hole is only slightly larger than the diameter of the operation rod 26. Thus if washer assembly 37 is depressed in one end it will bite into operating rod 26 much as does washer assembly 35.
U.S. Pat. No. 3,381,861, to Stein for a Gun for Applying Adhesives to Surfaces, shows a slidable plunger tube 20 passing through a gun housing 19 in which a plunger release member 35 has inner and outer ends 36 and 37. The inner end engages a notch 38 in the housing wall. The member 35 is apertured to fit around the tube 20 to clamp the tube while the member 35 is in an unreleased position. The outer end 37 extends beyond the housing for manual release of the member 35. A plunger rod feed washer 39 is mounted on the tube 20 and retained between coils of plunger feed spring 40. The washer 39 serves as a holding clamp on the plunger tube 20. The upper end of the spring 40 bears against the plunger release member 35 and the lower end bears on the bottom of the housing 19. When a lever 41 is manipulated by gripping the lever and a rigid grip 44 and squeezing the lever toward the grip to cause lever end 42 to bear down on washer 39 and spring 40, the plunger tube 20 is moved to cause an adhesive to be pressed down into a pump. To stop the flow of the material through the pump, the operater depresses the plunger release member 35 by bearing down on the end 37. This releases the hold of the member 35 on the plunger tube 20 and due to the expansible urging of a spring 26 the tube 20 is raised, thereby relieving pressure on the adhesive and stopping its flow.
The following patents disclose systems of interest:
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